(a) Field of the Invention
This invention is concerned with novel crystalline ironborosilicates and their uses in the production of high-octane liquid hydrocarbons. More particularly, it relates to novel crystalline ironborosilicate zeolitic materials possessing catalytic properties and to conversion processes using such crystalline ironborosilicates.
(b) Description of the Prior Art
It has been demonstrated in the past that zeolitic materials, both natural and synthetic, and commonly referred to as molecular sieves, can have catalytic, sorption and separating properties. A number of existing processes such as catalytic cracking, methanol conversion, isomerisation of xylenes, alkylation of aromatics, exemplify the uses of these molecular sieve materials.
Typically represented by aluminosilicates, zeolites are structurally complex crystalline inorganic polymers based on an infinitely extending framework of AlO.sub.4 and SiO.sub.4 tetrahedra linked to each other by the sharing of oxygen atoms. This framework structure contains large and small cavities interconnected by channels as in the case of Y-type zeolites. These cavities and channels which are generally uniform in size are occupied by cations and water molecules. The cations may be mobile and therefore can undergo ion-exchange. In view of the mobility of the cations, it is believed that zeolitic materials behave like solid electrolytes. The water molecules may be removed reversibly by the application of heat, which in most cases leaves intact a highly porous crystalline structure. As the ratio of silica to alumina increases, the zeolitic material becomes progressively hydrophobic. Zeolites structurally related to ZSM-5 do not possess cavities; they have channel intersections and they are generally hydrophobic.
In terms of composition, zeolites can be regarded as being derived from silica. The substitution of some of the silicon atoms within the crystalline framework of the silica by trivalent aluminium, boron or iron atoms generates an anionic site in the environments of the aluminium atoms so that, in order to preserve electroneutrality, a cation such as that of the alkali or alkaline-earth metals is required. Considering the fact that tetra-coordinated aluminium atoms cannot share the same oxygen atom, it follows that y in the following empirical formula representing a typical zeolite cannot be less than 2: EQU M.sub.n/2 O:Al.sub.2 O.sub.3 :y SiO.sub.2.wH.sub.2 O
wherein M is a cation of valence n, y is 2 or greater and w is a value representing the water contained in the intracrystalline channel systems of the zeolite after synthesis or crystallization in nature.
Prior art developments have resulted in the synthesis of more than 150 zeolite types. To date, forty zeolite minerals are known.
Zeolites which belong to the Pentasil family are considered relevant to the present invention. More specifically, this invention relates to crystalline ironborosilicate zeolites which are structurally related to ZSM-5 zeolites.
U.S. Pat. No. 3,702,886 which is here considered relevant discloses the crystalline aluminosilicate ZSM-5 and the process of preparing the same. This patent teaches the preparation of a crystalline alumino or gallosilicate and a crystalline alumino or gallogermanate by reacting silicon oxide or germanium oxide with aluminium oxide or gallium oxide in a range of specific ratios under specified reaction conditions. The product obtained has a specific X-Ray diffraction pattern. This patent is therefore limited to alumino and gallosilicate as well as alumino and gallogermanates. Patents disclosing the synthesis of ZSM-11 and ZSM-12 are likewise limited in scope to crystalline alumino or gallosilicates or germanates which also provide specific X-Ray diffraction patterns.
The production of the ZSM materials makes use of a mixed base system wherein sodium aluminate and a silicon-containing material are allowed to react in the presence of sodium hydroxide and an organic base template such as a tetrapropylammonium hydroxide or bromide under specified reaction conditions to yield the crystalline aluminosilicates.
U.S. Pat. No. 3,328,119 which is considered relevant art, claims and teaches the process of preparing a crystalline aluminoborosilicate wherein the boria forms an integral part of the crystal framework structure of the zeolite material. However, the crystalline structure of the material is not related to the Pentasil family.
Another U.S. Pat. No. 4,269,813 which is considered more relevant to this invention discloses a class of crystalline borosilicates designated as AMS-1B and a process of preparing same. AMS-1B crystalline borosilicates are zeolitic materials which provide an X-Ray diffraction pattern similar to ZSM-5. This patent is limited in scope to borosilicates.
German Offonlegungsschrift No. 2,830,787 relates to crystalline alumino, boro, arseno, and antimony silicates having specified X-Ray diffraction patterns and to processes for preparing the same.
German Offenlegungsschrift No. 2,755,770 discloses the preparation of crystalline iron aluminosilicates and their uses.
Additional relevant prior art comprises U.S. Pat. Nos. 4,029,716 and 4,078,009 which relate to a crystalline aluminosilicate zeolite having a silica to alumina ratio of at least 12 and a constraint index within the range of 1 to 12 and containing boron in an amount of at least 0.2 weight percent as a result of a reaction of the zeolite with a boron-containing compound.